This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Circuit For Eliminating Echo And Side Tones In A Switching System earlier filed in the Korean Industrial Property Office on Dec. 23 1998, and there duly assigned Serial No. 98-57856 by that Office, a copy of which application is annexed hereto and simultaneously filed herewith.
1. Field of the Invention
The present invention relates to switching processes and systems generally, and, more particularly, to processes and circuits for eliminating echo and side tones by employing a message mode of a time switch in a switching system.
2. Description of the Related Art
It has been my observation that the phenomenon of ringing echo that occurs in a hands-free telephone communication through an external speaker and microphone installed in a telephone is generally caused by the voice of the far end user being fed back from the speaker to the microphone. In addition, the side tone (or sidetone) phenomenon seems to usually be caused by the voice of a party induced to his own speaker when there is no impedance matching in the hybrid converting from two lines to four lines in a conventional telephone. Thus, if the echo and side tones are not properly eliminated during hands-free communication through a conventional telephone, the voice of one party is often mixed with that of the other party, degrading the communication quality. Hence, the conventional telephone should be provided with an additional circuit for eliminating such echo and side tones, resulting in an increase in production cost.
An example of one effort in the art to provide a system for echo cancellation and reduction of side tone is found in U.S. Pat. No. 5,099,472 to Bruce L. Townsend et al. entitled Hands Free Telecommunication Apparatus And Method, incorporated herein by reference.
It is an object of the present invention to provide an improved telephone switching process and system.
It is another object to provide a switching system with a circuit for eliminating the echo phenomenon occurring during hands-free communication through a telephone.
It is still another object of the present invention to provide a switching system with a circuit for eliminating the side tones occurring during hands-free communication through a telephone.
According to an aspect of the present invention, a circuit, for eliminating echo and side tones in a switching system connecting first and second subscribers, comprises a first linear converter for converting pulse code modulation (i.e., xe2x80x9cPCMxe2x80x9d) data generated by the first subscriber into an analog signal in a read message mode of a time switch, a side tone canceling filter for eliminating the side tones from the analog signal produced by the first linear converter, a clipper for clipping the analog signal rid of the side tones, a first PCM converter for converting the output signal of the clipper into refined PCM data written into the time switch in a write message mode of the time switch and transferred to the second subscriber, a second linear converter for converting the PCM data generated by the second subscriber into an analog signal, an echo canceling filter for eliminating the echo from the analog signal produced by the second linear converter, and a second PCM converter for converting the analog signal rid of the echo into refined PCM data written into the time switch in the write message mode and transferred to the first subscriber.